Could not use Observable.of in RxJs 6 and Angular 6

Looks like cartant's comment is correct, the RxJS upgrade guide doesn't cover that method specifically but does say "Classes that operate on observables have been replaced by functions"

Which seems to mean all or most of those class methods like .of, .throw etc. have been replaced by a function

So instead of

import { Observable, of } from "rxjs";
Observable.of(this.purposes);

do

import { of } from "rxjs";
of(this.purposes);

rxjs 6

import { PreloadingStrategy, Route } from '@angular/router';
import { Observable, of } from 'rxjs';

export class SelectivePreloadingStrategy implements PreloadingStrategy {
    preload(route: Route, load: Function): Observable<any> {
       return route.data && route.data.preload === false ? of(null) : load();
    }

 }